This makes me want to add metal to the resin and make my own thow-away air-cooled engines. Throw a rod? Print a new one! Need to port your heads for a new intake? Do some 3d work, print your new head.

I know, I'm dreamin'. But how cool would that be?

You can change the density of water with more than just salt. I bet it would work with cornstarch, which washes off.